The primary objective of this study is to evaluate the effect of Flolan infusions on exercise capacity in patients with pulmonary hypertension secondary to the scleroderma spectrum of diseases. This study also will evaluate the safety of continuous infusions of Flolan plus conventional therapy in this patient population. Other objectives of this study are to evaluate the effects of Flolan infusions on cardiopulmonary hemodynamic measurements, clinical signs and symptoms of pulmonary hypertension and the scleroderma spectrum of diseases, and survival in patients with pulmonary hypertension secondary to the scleroderma spectrum of diseases.